Estimates for the sensitivity and false-positive rates for second trimester serum screening for Down syndrome and trisomy 18 with adjustment for cross-identification and double-positive results.

Second trimester screening for fetal Down syndrome and trisomy 18 is available through separate protocols that combine the maternal age-specific risk and the analysis of maternal serum markers. We have determined the extent to which additional Down syndrome affected pregnancies may be identified through trisomy 18 screening, and the extent to which additional cases of trisomy 18 may be screen-positive for Down syndrome. The combined false-positive rate, taking into consideration those pregnancies that are screen-positive by both protocols, has also been determined. Sensitivity and false-positive rates were determined by computer simulation of results that incorporated previously published statistical variables into the model. Using second trimester risk cut-offs of 1:270 for Down syndrome and 1:100 for trisomy 18, it was found that few additional cases of Down syndrome are identified through trisomy 18 screening. However, approximately 6-10% of trisomy 18 affected pregnancies will be screen-positive for Down syndrome but screen-negative for trisomy 18. For women aged 40 or more, the false-positive rate for trisomy 18 exceeds 1% and approximately half of these cases will also be screen-positive for Down syndrome. For a population with maternal ages equivalent to that in the United States in 1998, after adjusting for the cross-identification, the sensitivity for three-analyte trisomy 18 screening is 78%. If this testing is performed in conjunction with Down syndrome "triple" screening, the Down syndrome sensitivity is 75% and the combined false-positive rate is 8.5%. If the three-analyte trisomy 18 screening is performed with the Down syndrome "quad" screen, the trisomy 18 sensitivity remains at 78%, the Down syndrome sensitivity is 79%, and combined false-positive rate is 7.5%. Sensitivity and false-positive rates are also provided for other widely used Down syndrome and trisomy 18 risk cut-offs. Sensitivity and false-positive rates that take into consideration cross-identification and double-positives should be helpful for pre-test counseling and the evaluation of serum screening programs.

Benn PA ，Ying J ，Beazoglou T ，Egan JF ... -  《PRENATAL DIAGNOSIS》

Sequential pathways of testing after first-trimester screening for trisomy 21.

Platt LD ，Greene N ，Johnson A ，Zachary J ，Thom E ，Krantz D ，Simpson JL ，Silver RK ，Snijders RJ ，Goetzl L ，Pergament E ，Filkins K ，Mahoney MJ ，Hogge WA ，Wilson RD ，Mohide P ，Hershey D ，MacGregor S ，Bahado-Singh R ，Jackson LG ，Wapner R ，First Trimester Maternal Serum Biochemistry and Fetal Nuchal Translucency Screening (BUN) Study Group ... -  《OBSTETRICS AND GYNECOLOGY》

Effectiveness of combining maternal serum alpha-fetoprotein and hCG in a second-trimester screening program for Down syndrome.

Mooney RA ，Peterson CJ ，French CA ，Saller DN Jr ，Arvan DA ... -  《OBSTETRICS AND GYNECOLOGY》

First- and second-trimester screening: detection of aneuploidies other than Down syndrome.

Breathnach FM ，Malone FD ，Lambert-Messerlian G ，Cuckle HS ，Porter TF ，Nyberg DA ，Comstock CH ，Saade GR ，Berkowitz RL ，Klugman S ，Dugoff L ，Craigo SD ，Timor-Tritsch IE ，Carr SR ，Wolfe HM ，Tripp T ，Bianchi DW ，D'Alton ME ，First and Second Trimester Evaluation of Risk (FASTER) Research Consortium ... -  《OBSTETRICS AND GYNECOLOGY》

Triploidy identified through second-trimester serum screening.

To describe the maternal serum marker patterns of triploid pregnancies and estimate the second-trimester prevalence of triploidy. Forty-two cases of triploidy were identified in six serum screening programmes, five in the United Kingdom, one in Canada. This study describes the serum marker patterns, serum screening results for Down syndrome, trisomy 18 and open neural tube defects, and maternal age of these triploidy cases. The risk cut-off levels were > or = 1 in 250 for Down syndrome, > or =2.5 MoMs alpha-fetoprotein for open neural tube defects and > or =1:100 for trisomy 18 screening. The estimated second-trimester prevalence of triploidy was based on 22 triploidy cases ascertained in 599 934 pregnancies from three routine screening programmes, which attempted complete ascertainment of aneuploidy cases. The observed second-trimester rate of triploidy was 0.37 per 10 000 fetuses. Two different serum marker patterns were seen in triploid pregnancies, distinguished from each other by typically very high or very low levels of total hCG or free beta-hCG. The median maternal ages were respectively 33 years for triploidy with human chorionic gonadotrophin levels < 1.0 MoM, and 26 years for those with hCG levels > or =1.0 MoM. Fifty-seven percent of the pregnancies with a triploid fetus had a risk estimate > or =1:100 for trisomy 18 alone, 10% had an alpha-fetoprotein > or =2.5 MoM, 5% were screen positive for Down syndrome alone, and 19% had an increased risk or positive results for more than one anomaly. The simultaneous use of maternal serum tests designed to screen prenatally for Down syndrome, neural tube defects, and an increased risk of trisomy 18 resulted in a screen-positive result for 90% of pregnancies with triploidy.

Huang T ，Alberman E ，Wald N ，Summers AM ... -  《PRENATAL DIAGNOSIS》